In distributed process processing with more than one computer, a technological example in which a process monitoring daemon in a computer sends a heartbeat message periodically to determine if there is abnormality in others is disclosed in Japanese Patent Application Laid-Open No. 1997-319720. Also as a technology related to the present invention, a bridge for mesh type networks using a spanning tree protocol (STP) is disclosed in Japanese Patent Application Laid-Open No. 2004-201140.